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Analog-to-digital conversion as a source of drifts in displacements derived from digital recordings of ground acceleration

Bulletin of the Seismological Society of America

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Abstract

Displacements obtained from double integration of digitally recorded ground accelerations often show drifts much larger than those expected for the true ground displacements. These drifts might be due to many things, including dynamic elastic ground tilt, inelastic ground deformation, hysteresis in the instruments, and cross feed due to misalignment of nominally orthogonal sensors. This article shows that even if those effects were not present, the analog-to-digital conversion (ADC) process can produce apparent "pulses" and offsets in the acceleration baseline if the ground motion is slowly varying compared with the quantization level of the digitization. Such slowly varying signals can be produced by constant offsets that do not coincide with a quantization level and by near- and intermediate-field terms in the wave field radiated from earthquakes. Double integration of these apparent pulses and offsets leads to drifts in the displacements similar to those found in processing real recordings. These effects decrease in importance as the resolution of the ADC process increases.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Analog-to-digital conversion as a source of drifts in displacements derived from digital recordings of ground acceleration
Series title:
Bulletin of the Seismological Society of America
Volume
93
Issue:
5
Year Published:
2003
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
2017
Last page:
2024
Number of Pages:
8